Permanent magnet motors are classified for example into a rotating armature type with a permanent magnet arranged on the side of a stator, and a rotating field type with a permanent magnet arranged on the side of a rotor. In a motor of the rotating field type, linkage of magnetic flux generated by a permanent magnet (hereinafter referred to as a “magnet”) of a rotor with a coil on the side of a stator is generated to thereby rotate the rotor.
A particular structure of a rotor of the rotating field motor is such that a magnet is buried in a core that extends in a direction of a rotation axis, and a pole face of the magnet extends in the direction of the rotation axis.
Techniques relevant to the present invention are introduced in the following publications.
Japanese Patent Application Laid-Open No. 11-234931 (1999)
Japanese Patent Application Laid-Open No. 2000-209799
Japanese Patent Application Laid-Open No. 2001-37119
In a rotor disclosed in patent publications listed above, an end of a magnet defined in a direction of a rotation axis is depressed or flat with respect to an end of a core defined in the same direction. This causes magnetic flux generated by the magnet to be short-circuited from one pole face to another pole face of the same magnet by passing through the end of the magnet.
FIGS. 31 and 32 show a short circuit of magnetic flux generated in a conventional rotor by magnetic lines of force. In FIG. 31, an end of a magnet is depressed with respect to an end of a core. In FIG. 32, an end of a magnet is flat with respect to an end of a core.
When a short circuit of magnetic flux is generated in a rotor, magnetic flux passing from the rotor to a stator is reduced to cause reduction of drive efficiency or drive output of a motor.
The present invention has been made in view of the above-discussed circumstances. The present invention is intended to prevent a short circuit of magnetic flux in a rotor.